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1. Field of the Invention
This invention relates generally to the field of wireless communications and includes telecommunications and automatic position-locating equipment attached to an aircraft secured to the surface. More particularly, this invention is useful for accurately evaluating wireless field strengths at various elevations of potential wireless base station sites.
2. Description of the Related Art
Wireless communication has experienced explosive growth. In just a few years cellular telephone usage has soared, and more growth is planned as wireless Internet access improves. This explosive growth has revolutionized data and voice communication.
This explosive growth, however, presents a challenge for wireless service providers. As cellular communication soars in use, more cellular base stations are required. These base stations house equipment for transmitting, receiving, and processing wireless communications to a communications network. Each base station covers a geographic sector, or xe2x80x9ccell,xe2x80x9d and each cell varies in size depending upon the terrain and the number of users. As use of wireless services grows, more cells are needed and, hence, more base stations are required.
Choosing the location for a new base station, however, is extremely complicated. The location of the base station largely determines the quality and range of the cell""s signal coverage. The location of the base station is important because radio waves propagate according to natural laws and not city boundaries. See NEIL J. BOUCHER, THE CELLULAR RADIO HANDBOOK 42 (1995). The tall buildings of urban areas, for example, can both confine radio waves and also cause reflections. See id. at 44. Thus the final location of a base station is often a process of evaluating many potential sites and choosing the location that offers the best compromise of many considerations. See PAUL BEDELL, CELLULAR/PCS MANAGEMENT 24-27 (1999).
Often these potential base station sites are located atop urban buildings or radio towers. Engineers must somehow evaluate the quality and range of a base station signal transmitted from atop a selection of potential buildings or towers. As most cellular designers recognize, the most reliable field strength measurements are obtained when signals are broadcast from the actual site itself (e.g., the roof of the desired building). The field strengths could be estimated using mathematical formulae, but these formulae require several correction factors. See BOUCHER, supra, at 59. An actual transmission from or near the potential site, called a xe2x80x9csurvey,xe2x80x9d is therefore necessary to accurately evaluate cellular transmission and reception.
A method of evaluating the communication paths of an elevated antenna uses a crane or cherry picker. The conventional method involves bringing a large crane or cherry picker to the potential base station site, and hoisting a boom with an attached antenna to a selected elevation. A transmission is made from the antenna at that elevation, and the field strengths of the transmission are measured at various points within the potential cell.
A crane/cherry-picker, however, is an impractical method of hoisting the antenna. Cranes and cherry pickers, because of their large size, are cumbersome. This heavy equipment is extremely difficult to maneuver within tight, urban locations. Cranes and cherry-pickers also block large portions of any roadway and exacerbate traffic congestion. Bridges and low-clearance tunnels may pose delivery concerns. Utility lines may need to be removed and rerouted to accommodate the boom""s large size. Cranes and cherry-pickers, in short, are so large that this conventional method is often impractical.
Cranes and cherry-pickers are also very expensive to operate. Because this heavy equipment must often be rented from an independent operator, the rental charges can be hundreds of dollars per hour. Any removed and/or rerouted utility lines are an added and unnecessary expense that increase the cost of a survey. Cranes and cherry-pickers, in fact, have been said to unnecessarily double the cost of any survey. See BOUCHER, supra, at 87.
Cranes and cherry-pickers also frequently result in unexpected expenses. Cost overruns occur despite even the best projections. The weight of heavy equipment often damages blacktop streets. Water mains and gas mains can rupture from this same weight. Buildings are damaged from an errant boom or hoisted antenna. The antenna itself has been known to unexpectedly release and fall from the boom. Falling antennas obviously endanger both workers and pedestrians.
Another method of evaluating the signal strength of a potential base station site uses a helicopter. The helicopter lifts the antenna to the desired elevation and hovers while field strength measurements are performed. A helicopter, however, is extremely expensive and its costs are usually only justified for remote and undeveloped mountainous locations or for locations over water.
A final method of evaluating the signal strength of a potential base station site utilizes alternative air vehicles. See BEDELL, supra, at 25; BOUCHER, supra, at 87. For example, transmitting equipment is attached to a blimp or to a balloon that is tethered at the potential base station site and floated to the desired height. While balloons can be easily floated to the desired height, this method, however, is very susceptible to gusting wind. Although the blimp or balloon can be tethered by multiple ropes, the increased number of ropes alters the aerodynamics and causes the balloon or blimp to sway and dive during gusts of wind. Thus, conventional methods using alternative air vehicles have not yielded reliable field strength measurements.
The conventional methods described above are inherently inefficient. There is, accordingly, a need for an apparatus which can quickly be used to measure cell site field strength, which is easy to maneuver between potential cell sites, which promotes efficient field strength testing, and which is cost effective to implement.
The aforementioned problems are minimized by using mobile, lightweight transmission and position-locating test equipment that is securely housed in a protective carrier and attached to an aircraft secured to the surface, such as a balloon securely tethered with guide equipment to a flatbed truck. This transmission and position-locating test equipment is used to accurately evaluate field strengths at various elevations of potential base station sites. Once the survey measurements are completed for the site, the air/surface test equipment is quickly and easily relocated to the next potential site. The air/surface test, therefore, provides much quicker testing than conventional methods.
The test equipment makes use of and includes a transmitter, an antenna, and an automatic position-locating system. In a preferred embodiment, the total weight of the test equipment, the protective carrier, and the stabilizing equipment used to securely attach and position the protective carrier to the aircraft is less than fifty-five pounds. Further, the test equipment may be powered by a connected cable that runs from a surface generator along a tether to the aircraft.
The aircraft of the air/surface test may be tethered to a ground transportation vehicle, such as a truck that can navigate over roads and highways, or it may be tethered to a water transportation vehicle, such as a boat that can navigate waterways. Alternatively, the aircraft may be tethered to the surface itself, such as, for example securing a tether(s) to the ground with a stake(s). Guide equipment for securely attaching and positioning the aircraft from the surface includes one or more tethers, a winching system connected to a tether that is used to raise and lower the aircraft, optionally, one or more pulleys to guide additional tethers (when multiple tethers are used), and additional equipment to securely affix and anchor the tether(s) to the surface terrain or to the surface vehicle.
The aircraft of the air/surface test may be a helium balloon or a blimp that is large enough to support the test equipment. Once inflated, a helium balloon or blimp could be used to conduct surveys for up to 48-72 hours (depending on the shelf-life of the helium). Further, the air/surface test system may include safety devices, such as, for example, a strobe light on the aircraft or a tear away device that automatically deflates a balloon or blimp if a tether(s) is severed.
In a preferred embodiment, the air/surface test makes use of and includes a helium balloon that is tethered to three fold-out arms on a flatbed truck. The fold-out arms extend approximately fifteen to twenty feet from the middle of the truck""s flatbed and are positioned in a triangular arrangement from each other. A winching system is affixed on the flatbed and connected to a tether at the end of ones of the arms. The other two tethers are connected to the ends of the other two arms with pulley systems.
The transmitter produces test propagation signals that are selectively broadcast from the antenna. The position-locating system receives and broadcasts signals that are used to calculate near-precise positioning data, such as longitude, latitude, altitude, time, geographic position, speed, and direction of travel data, associated with the test equipment. Thus, the field strengths as well as the positioning data are measured and recorded each time a reading from the test equipment is taken, and they are used to reconcile aerodynamic and elevation changes, such as changes caused by swaying and/or diving during gusts of wind, to provide reliable field strength data for locating potential base station sites. In addition, communications network interface equipment may be used to process and reconcile the test propagation and position-locating signals.
The air/surface test broadcasts various test propagation signals and position-locating signals. Test propagation signals may include the Industrial, Scientific, and Medical (ISM) Band frequencies, such as, 2.4-2.5 GHz, cellular telephone frequencies, such as, 806-960 MHz, 1710-1855 MHz, and 2500-2690 MHz, paging frequencies, digital processing frequencies, and any other frequency in the electromagnetic spectrum. The type of antenna used to transmit the test signals may be directional or omnni-directional. In addition, the type of automatic position-locating system used is preferably a global positioning system (GPS).
The air/surface test is significantly less expensive than conventional methods. Because the air/surface test system is the first mobile, self-contained apparatus that makes use of an aircraft securely attached to a transportation vehicle for evaluating potential sites, it eliminates the costly and unnecessary rental expenses of using conventional systems, such as a crane or cherry picker. The mobile, flexible design of the air/surface test system also substantially eliminates the unexpected damage-related expenses of the cumbersome conventional methods.
The air/surface test also yields more efficient testing. Because the air/surface test system is mobile and self-contained, the air/surface test system can be quickly and easily moved between potential cell site locations. Also, because the air/surface test system may include an aircraft tethered to a boat, the air/surface test system can be used to test potential cell sites above aquatic terrain. Further, the air/surface test allows cellular designers to conduct more tests in a work week, and the designers can quickly and easily move the air/surface test system to the next potential location. The air/surface test thus promotes more efficient testing, and the total cost of a survey is substantially reduced.